1. Field of the Invention
This invention relates to a method and apparatus for acquiring a line signal. This invention particularly relates to a method and apparatus for acquiring a line signal, wherein the line signal is acquired by use of a plurality of charge coupled device sensors, which are arrayed linearly.
2. Description of the Related Art
There have heretofore been known image read-out apparatuses, wherein a line signal representing image information, which is carried along each line on an image storage sheet to be subjected to image readout, is acquired from the image storage sheet by use of a charge coupled device sensor (hereinbelow referred to as the CCD sensor), which comprises a plurality of light receiving pixels arrayed linearly. In the image read-out apparatuses for reading out the image information from the image storage sheet, it is necessary for the CCD sensor to have a length corresponding to a width of the image storage sheet. However, it is not always possible to make a long CCD sensor. Therefore, for example, a plurality of CCD sensors are arrayed linearly and located such that end regions of CCD sensors, which are adjacent to each other, overlap one upon the other with respect to a direction intersecting with the linear array direction of the CCD sensors. In this manner, a long CCD sensor unit comprising the plurality of the CCD sensors is formed. Light, which carries the image information along each line on the image storage sheet, is received by the long CCD sensor unit and subjected to photoelectric conversion with respect to each of light receiving pixels constituting the long CCD sensor unit. In this manner, a signal charge corresponding to each of the light receiving pixels constituting the long CCD sensor unit is obtained. The thus obtained signal charges corresponding respectively to the light receiving pixels are read, and the line signal is thereby acquired.
With respect to the end regions of the CCD sensors adjacent to each other, which end regions overlap one upon the other, an arithmetic mean calculation is made on a value (a signal component) obtained from the signal charge having been obtained from a certain light receiving pixel, which is located at the end region of one of the CCD sensors adjacent to each other, and a value (a signal component) obtained from the signal charge having been obtained from a light receiving pixel, which is located at the end region of the other CCD sensor and overlaps upon the aforesaid certain light receiving pixel of the one CCD sensor with respect to the direction intersecting with the linear array direction of the CCD sensors. The thus calculated arithmetic mean value is taken as the signal component of the line signal, which signal component represents the light information received at the end regions of the CCD sensors adjacent to each other.
The long CCD sensor unit described above is often employed for detection of radiation images in radiation image read-out apparatuses. With the radiation image read-out apparatuses utilizing the long CCD sensor unit, stimulating rays are irradiated to a stimulable phosphor sheet comprising a stimulable phosphor layer, on which a radiation image of an object, such as a human body, has been stored. The stimulating rays cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to radiation. The light emitted by the stimulable phosphor sheet is received by the long CCD sensor unit and subjected to photoelectric conversion. Signal charges, which have been obtained from the photoelectric conversion of the emitted light, are read, and a line signal is thereby obtained. The thus obtained line signal is then processed and utilized for the reproduction of the radiation image of the object as a visible image on a recording material.
The light emitted by the stimulable phosphor sheet is weak. In order for the radiation image information of the object, which radiation image information is represented by the light emitted by the stimulable phosphor sheet, to be acquired with a high signal-to-noise ratio, it is desired that the signal charges, which have been obtained from the photoelectric conversion of the emitted light having been received by the long CCD sensor unit, be subjected to binning processing with respect to the linear array direction of the CCD sensors and thereby be read.
However, the plurality of the CCD sensors, which are arrayed linearly in the long CCD sensor unit, are located such that the end regions of the CCD sensors adjacent to each other overlap one upon the other with respect to the direction intersecting with the linear array direction of the CCD sensors. Therefore, there is the risk that, when the binning processing is performed on the signal charges having been transferred from the plurality of the light receiving pixels constituting the CCD sensors, the position of one unit of the light receiving pixels, from which one unit of the signal charges to be subjected together to the binning processing have been transferred, in one of the CCD sensors adjacent to each other and the position of one unit of the light receiving pixels, from which one unit of the signal charges to be subjected together to the binning processing have been transferred, in the other CCD sensor will shift from each other in the linear array direction of the CCD sensors. If the position of the one unit of the light receiving pixels, which are to be subjected together to the binning processing, in one of the CCD sensors adjacent to each other and the position of the one unit of the light receiving pixels, which are to be subjected together to the binning processing, in the other CCD sensor shift from each other in the linear array direction of the CCD sensors, there will be the risk that the phase determined by the sampling period represented by the intervals of the respective units of the light receiving pixels, which are to be subjected together to the binning processing, the intervals being taken along the linear array direction of the CCD sensors, will vary for the CCD sensors adjacent to each other. Also, in such cases, there will be the risk that, with respect to the end regions of the CCD sensors adjacent to each other, which end regions overlap one upon the other, the value (the signal component) obtained from the one unit of the signal charges, which have been obtained from the photoelectric conversion of the light received at a certain position with respect to the linear array direction of the CCD sensors, and the value (the signal component) obtained from the one unit of the signal charges, which have been obtained from the photoelectric conversion of the light received at a position different from the aforesaid certain position with respect to the linear array direction of the CCD sensors, will be subjected to the arithmetic mean calculation. As a result, a signal component, which accurately represents one unit of the image information, cannot be acquired. Accordingly, the problems occur in that a line signal carrying accurate position information cannot be acquired.